Catenary anchored or dynamically positioned vessels for development of oil and gas fields must be designed for good stability during severe wind and wave conditions, wherein minimal movements during different work operations is a necessity, together with security, availability and good housing conditions on these vessels. A design having increased stability and reduced motions also reduces the loads on the anchoring means.
The economical aspects of these kinds of vessels amounts to the strive towards largest possibly pay load on the work deck, i.e. equipment, machines and supplies within the decided concept. Normally an increase in pay load results in increased motion of the vessel. Therefore, when the pay load near to the work deck is increased, usually also the complete steel structure must be amplified. These difficulties present to the designer the task of either designing a new vessel or modernizing an existing vessel.